/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlinePartyInterface.h
Returns the json version of a join info for a current party
[FString](API\Runtime\Core\Containers\FString) MakeJoinInfoJson ( const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & LocalUserId, const [FOnlinePartyId](API\Plugins\OnlineSubsystem\FOnlinePartyId) & PartyId )